Tribochemical and Thermochemical Reactions of Stearic Acid on Copper Surfaces Studied by Infrared Microspectroscopy

The tribochemistry of copper with stearic acid was studied using a pin-on-disc wear tester under boundary lubrication conditions. Wear, as measured by surface profilometry, indicated that stearic acid was able to reduce the wear fourfold. Surface analysis by Fourier Transform Infrared (FTIR) microspectroscopy revealed that cupric stearate was formed during the rubbing process by tribochemical reactions. The reaction product was confirmed by model compounds and was also found to be comparable with those from the static thermal experiments of stearic acid on copper surface at 140°C-160°C. The affinity between the chemisorbed stearic acid and bidentate copper stearate complex is believed to be responsible for the formation of a protective film on the copper surfaces to reduce the wear from further propagation.